The recent prior art contains many disclosures describing mercaptoacyl derivatives of amino acids. Exemplary of these disclosures is U.S. Pat. No. 4,105,776, issued Aug. 8, 1978, which discloses compounds having the formula ##STR5## wherein, inter alia, R.sub.e is hydrogen, acyl or ##STR6## R.sub.f and R.sub.g each is hydrogen, lower alkyl, phenyl or phenyl-lower alkyl; R.sub.h is hydrogen, hydroxy or lower alkyl; R.sub.i is hydroxy, NH.sub.2 on lower alkoxy; p is 0, 1 or 2; and q is 1, 2 or 3. The compounds are described as angiotensin converting enzyme inhibitors, useful in the treatment of hypertension.